The present invention relates to the signal processing within, radar and sonar or an ultrasonar equipment and more particularly the invention relates to the signal processing of radar ultrasonic or sonic pulses which have responded to an object as the equipment has approached that object to a particular distance (or vice versa) under utilization of in phase and quadrature phase features of a Doppler signal.
It is known to use dragged vehicles (drones) to represent air targets. This kind of equipment is used for training exercises or the like. The dragged target or drone is equipped with e.g. radar which responds to the passing of projectiles that is to projectiles passing the target at a particular distance. A particular sensitive target zone may for example be defined by a hypothetical body having a distance between 1.5 and 10 m from the target or one can say that the sensitive zone is a sphere of a radius having that dimension around the center of the target. The on board system here is comprised of the radar front end with a omnidirecitonal transmitter and receiver antenna; at least omnidirectionality is desired as far as and to the utmost extent possible, and further included are signal processor and a telemetric transmitter to transmit to the ground coded information concerning hits or miss and by how much.
U.S. Pat. No. 3,878,526 describes a radar evaluating circuit wherein diffentiation is provided for the in phase or I signal, and the quadrature or Q signal and the differentiated signal is multiplied with the respective other undifferentiated signal, and the sum of these products is integrated in order to provide and extract a signal that is representative of the target motion.
U.S. Pat. No. 4,499,467 describes another analogous radar signal processing stage wherein in phase or I signal and quadrature or Q signals are processed through phase shifting elements. Generally it has to be said that the acquisition characteristics is of spherical configuration with rather sharp outer boundaries which results from the fact that the transmitter pulse being only a few nanoseconds wide is on return acceptable only beyond a certain signal gate timing, assuming furthermore that the transmitter signal is truly omnidirectional.
In the case of a hit signal pursuant to a passage of a projectile through the acquisition characteristics three conditions have to be met simultanesously. First the approach speed, that is the relative speed between the projectile and the antenna, center, i.e. the center of gravity of the antenna, must be within particular upper and lower limits. Second, the projectile's trajectory within the acquisition characteristics is equal to or larger than a predetermined minimum path lengths. Thirdly, the echo amplitude of the projectile exceeds a particular threshold value, applicable to the minimum path length.
The extraction of the signal parameters needed to obtain the hit/miss differentiation and using the raw Doppler signal poses the following problems. The raw signal of course appears superimposed with noise resulting from the physically vibrating parts of the dragged target. This is also known as radar microphony. Any on-board, real time signal processing is essential simply because one cannot transmit raw data in its entirety for reasons of practical constraints posed by the capacity of telemetric equipment. Extensive and expensive filter methods such as FFT filters and/or Doppler filter banks are too expensive. Because the equipment must be relatively cost effective owing to the possibly frequent loss. The failure rate and incorrect alarm rate of automatic hit detection must in fact be zero; in other words it is simply unacceptable to have incorrect hit/miss rate distinction.